usb: dwc3: return error code from the most recent call

Copy-paste error from the previous block of error handling code.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
expression e,e1;
@@

if (IS_ERR(e)) {
  ...
(
  ret = PTR_ERR(e);
|
*  ret = PTR_ERR(e1);
)
  ...
  return ret;
}
// </smpl>
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/dwc3-st.c

@@ -243,7 +243,7 @@ static int st_dwc3_probe(struct platform_device *pdev)
 	dwc3_data->rstc_rst = devm_reset_control_get(dev, "softreset");
 	if (IS_ERR(dwc3_data->rstc_rst)) {
 		dev_err(&pdev->dev, "could not get reset controller\n");
-		ret = PTR_ERR(dwc3_data->rstc_pwrdn);
+		ret = PTR_ERR(dwc3_data->rstc_rst);
 		goto undo_powerdown;
 	}